Recent Advances on Surface-modified Biomaterials Promoting Selective Adhesion and Directional Migration of Cells

A new era for applications of multi-principal element alloys in the biomedical field

In today's context of an aging population and the gradual decline of human physiological functions, we are increasingly confronted with health issues such as fractures and arthritis. The demand for implants has risen correspondingly, while traditional alloys have become insufficient to meet the developmental needs of this era. The emergence of multi-principal element alloys (or high-entropy alloys) in 2004 has attracted significant attention, leading to extensive research due to their remarkable four core effects. Currently, multi-principal element alloys are gradually demonstrating their potential in the biomedical field. Therefore, a review of multi-principal element alloys in biomedical applications is of high interest. This paper explores the key considerations in the design of biological multi-principal element alloys, focusing on the latest research advancements in areas such as orthopedic implants, dentistry, and cardiovascular stents. We analyze their advantages in mechanical properties and biocompatibility while introducing their preparation methods. Furthermore, the article discusses the challenges faced by biological multi-principal element alloys in current research and anticipates future development directions for these materials. The primary objective of this review is to show the potential applications of multi-principal element alloys in implants, ensuring that the discussion remains engaging and novel. We aim to provide a reference to facilitate development of multi-principal element alloys for practical applications in the biomedical field.

Photocleavage and Photophysical Properties of Amine Releasing BODIPY Derivatives

To date, there is still a lack of suitable methods for chemical modification of graphene surfaces in situ. Photocleavable compounds have great potential for in situ modification of chemical species with visible light, leaving desired chemical functionalities on the surface. Green light-sensitive boron dipyrromethene (BODIPY) derivatives can release diverse cargos, including biologically important amines. In this study, green light-sensitive photocleavable BODIPY derivatives with different aromatic anchors for surface binding were designed and synthesized with the ultimate goal of selective graphene surface patterning. The effects of different aromatic anchor groups on photocleaving capability, their structural and photophysical properties and photocleavage in different conditions were studied. Photocleavage was significantly faster, and more controllable photoreaction was achieved in inert conditions than in the presence of oxygen (ambient air). In addition, pyrene as an anchor lowered fluorescence quantum yield and intensities of absorption and emission maxima of the entire BODIPY derivative, making it a poorer fluorophore than the derivatives with the naphthalene and phenyl anchors.

Biointerface engineering through amalgamation of gene technology and site-specific growth factor conjugation for efficient osteodifferentiation

The development of bone implants through bioinspired immobilization of growth factors remains a key issue in the generation of biological interfaces, especially in enhancing osteodifferentiation ability. In this study, we developed a strategy for surface functionalization of poly(lactide-glycolide) (PLGA) and hydroxyapatite (HA) composite substrates through site-specific conjugation of bone morphogenetic protein 2 containing 3,4-hydroxyphenalyalanine (DOPA-BMP2) mediated by tyrosinase and sortase A (SrtA). Firstly, the growth factor BMP2-LPETG containing LPETG motif was successfully expressed in Escherichia coli through recombinant DNA technology. The excellent binding affinity of binding growth factor (DOPA-BMP2) was achieved by converting the tyrosine residue (Y) of YKYKY-GGG peptide into DOPA (X) by tyrosinase, which bound to the substrates. Then its GGG motif was specifically bound to the end of BMP2-LPETG mediated by SrtA. Therefore, the generated bioactive DOPA-BMP2/PLGA/HA substrates significantly promoted the osteogenic differentiation of MC3T3-E1 cells. Thanks to this microbial-assisted engineering approach, our work presents a facile and highly site-specific strategy to engineer biomimetic materials for orthopedics and dentistry by effectively delivering growth factors, peptides, and other biomacromolecules.

Micro-fluidic covalent immobilization of multi-gradient RGD peptides on a gelatin surface for studying endothelial cell migration

Collective endothelial migration is a hallmark of wound healing, which is regulated by spatial concentration gradients of extracellular biochemical factors. Arginine-glycine-aspartate (RGD) peptides play a vital role in regulating cell migration through specific binding to integrins. In this study, a micro-fluidic technology combined with a photopolymerization technique is developed to create gelatin methacryloyl (GelMA)-based substrates with various concentration gradients of RGD peptides. The capability of generating linear and nonlinear RGD concentration gradients was quantitatively verified through numerical simulation and immunohistochemical quantitative experiments. The results of the concentration gradients show a strong concurrence between the immunohistochemical quantification experiments and numerical simulations. Furthermore, endothelial migration experiments were conducted with various concentration gradients of RGD peptides. We have observed that endothelial cells on the surface of gels with a linear concentration gradient exhibit a larger cell area, a longer cell perimeter, and more stress fiber density. Furthermore, the cells demonstrate directional alignment and migration towards regions with a higher RGD concentration. High concentration gradients significantly enhance endothelial cell migration, consistent with observations on surfaces of gels with nonlinear concentration gradients. In brief, we proposed a simple and effective micro-fluidic photopolymerization technique capable of generating diverse concentration gradients of RGD and probing their effects on cell migration. The results suggest that regulating the RGD peptide concentration gradients can alter the migration of endothelial cells, showing potential for promoting wound healing.

Gradient Functionalization of Poly(lactic acid)-Based Materials with Polylysine for Spatially Controlled Cell Adhesion

The development of biomaterials with gradient surface modification capable of spatially controlled cell adhesion and migration is of great importance for tissue engineering and regeneration. In this study, we proposed a method for the covalent modification of PLA-based materials with a cationic polypeptide (polylysine, PLys) via a thiol-ene click reaction carried out under a light gradient. With this aim, PLA-based films were fabricated and modified with 2-aminoethyl methacrylate (AEMA) as a double bond source. The latter was introduced by reacting pre-formed and activated surface carboxyl groups with the amino group of AEMA. The success of the modification was confirmed by 1H NMR, Raman and X-ray photoelectron spectroscopy data. A further photoinduced thiol-ene click reaction in the presence of a photosensitive initiator as a radical source was further optimized using cysteine. For grafting of PLys via the thiol-ene click reaction, PLys with a terminal thiol group was synthesized by ring-opening polymerization using Cys(Acm) as an amine initiator. Deprotection of the polypeptide resulted in the formation of free thiol groups of Cys-PLys. Successful gradient grafting of Cys-PLys was evidenced by covalent staining with the fluorescent dye Cy3-NHS. In addition, PLys gradient-dependent adhesion and migration of HEK 293 cells on PLys-PLA-based surfaces was confirmed.

Endothelium-Mimicking Materials: A "Rising Star" for Antithrombosis

The advancement of antithrombotic materials has significantly mitigated the thrombosis issue in clinical applications involving various medical implants. Extensive research has been dedicated over the past few decades to developing blood-contacting materials with complete resistance to thrombosis. However, despite these advancements, the risk of thrombosis and other complications persists when these materials are implanted in the human body. Consequently, the modification and enhancement of antithrombotic materials remain pivotal in 21st-century hemocompatibility studies. Previous research indicates that the healthy endothelial cells (ECs) layer is uniquely compatible with blood. Inspired by bionics, scientists have initiated the development of materials that emulate the hemocompatible properties of ECs by replicating their diverse antithrombotic mechanisms. This review elucidates the antithrombotic mechanisms of ECs and examines the endothelium-mimicking materials developed through single, dual-functional and multifunctional strategies, focusing on nitric oxide release, fibrinolytic function, glycosaminoglycan modification, and surface topography modification. These materials have demonstrated outstanding antithrombotic performance. Finally, the review outlines potential future research directions in this dynamic field, aiming to advance the development of antithrombotic materials.

Biointerfaces with ultrathin patterns for directional control of cell migration

In the context of wound healing and tissue regeneration, precise control of cell migration direction is deemed crucial. To address this challenge, polydimethylsiloxane (PDMS) platforms with patterned 10 nm thick TiOx in arrowhead shape were designed and fabricated. Remarkably, without tall sidewall constraints, MC3T3-E1 cells seeded on these platforms were constrained to migrate along the tips of the arrowheads, as the cells were guided by the asymmetrical arrowhead tips which provided large contact areas. To the best of our knowledge, this is the first study demonstrating the use of thin TiOx arrowhead pattern in combination with a cell-repellent PDMS surface to provide guided cell migration unidirectionally without tall sidewall constraints. Additionally, high-resolution fluorescence imaging revealed that the asymmetrical distribution of focal adhesions, triggered by the patterned TiOx arrowheads with arm lengths of 10, 20, and 35 μm, promoted cell adhesion and protrusion along the arrowhead tip direction, resulting in unidirectional cell migration. These findings have important implications for the design of biointerfaces with ultrathin patterns to precisely control cell migration. Furthermore, microelectrodes were integrated with the patterned TiOx arrowheads to enable dynamic monitoring of cell migration using impedance measurement. This microfluidic device integrated with thin layer of guiding pattern and microelectrodes allows simultaneous control of directional cell migration and characterization of the cell movement of individual MC3T3-E1 cells, offering great potential for the development of biosensors for single-cell monitoring.

Recent Advances in Biomaterials-Based Therapies for Alleviation and Regeneration of Traumatic Brain Injury

Traumatic brain injury (TBI), a major public health problem accompanied with numerous complications, usually leads to serve disability and huge financial burden. The adverse and unfavorable pathological environment triggers a series of secondary injuries, resulting in serious loss of nerve function and huge obstacle of endogenous nerve regeneration. With the advances in adaptive tissue regeneration biomaterials, regulation of detrimental microenvironment to reduce the secondary injury and to promote the neurogenesis becomes possible. The adaptive biomaterials could respond and regulate biochemical, cellular, and physiological events in the secondary injury, including excitotoxicity, oxidative stress, and neuroinflammation, to rebuild circumstances suitable for regeneration. In this review, the development of pathology after TBI is discussed, followed by the introduction of adaptive biomaterials based on various pathological characteristics. The adaptive biomaterials carried with neurotrophic factors and stem cells for TBI treatment are then summarized. Finally, the current drawbacks and future perspective of biomaterials for TBI treatment are suggested.

RGD Nanoarrays with Nanospacing Gradient Selectively Induce Orientation and Directed Migration of Endothelial and Smooth Muscle Cells

Directed migration of cells through cell-surface interactions is a paramount prerequisite in biomaterial-induced tissue regeneration. However, whether and how the nanoscale spatial gradient of adhesion molecules on a material surface can induce directed migration of cells is not sufficiently known. Herein, we employed block copolymer micelle nanolithography to prepare gold nanoarrays with a nanospacing gradient, which were prepared by continuously changing the dipping velocity. Then, a self-assembly monolayer technique was applied to graft arginine-glycine-aspartate (RGD) peptides on the nanodots and poly(ethylene glycol) (PEG) on the glass background. Since RGD can trigger specific cell adhesion via conjugating with integrin (its receptor in the cell membrane) and PEG can resist protein adsorption and nonspecific cell adhesion, a nanopattern with cell-adhesion contrast and a gradient of RGD nanospacing was eventually prepared. In vitro cell behaviors were examined using endothelial cells (ECs) and smooth muscle cells (SMCs) as a demonstration. We found that SMCs exhibited significant orientation and directed migration along the nanospacing gradient, while ECs exhibited only a weak spontaneously anisotropic migration. The gradient response was also dependent upon the RGD nanospacing ranges, namely, the start and end nanospacings under a given distance and gradient. The different responses of these two cell types to the RGD nanospacing gradient provide new insights for designing cell-selective nanomaterials potentially used in cell screening, wound healing, etc.

Biomedical polymers: synthesis, properties, and applications

Biomedical polymers have been extensively developed for promising applications in a lot of biomedical fields, such as therapeutic medicine delivery, disease detection and diagnosis, biosensing, regenerative medicine, and disease treatment. In this review, we summarize the most recent advances in the synthesis and application of biomedical polymers, and discuss the comprehensive understanding of their property-function relationship for corresponding biomedical applications. In particular, a few burgeoning bioactive polymers, such as peptide/biomembrane/microorganism/cell-based biomedical polymers, are also introduced and highlighted as the emerging biomaterials for cancer precision therapy. Furthermore, the foreseeable challenges and outlook of the development of more efficient, healthier and safer biomedical polymers are discussed. We wish this systemic and comprehensive review on highlighting frontier progress of biomedical polymers could inspire and promote new breakthrough in fundamental research and clinical translation.

Alleviating Oxidative Injury of Myocardial Infarction by a Fibrous Polyurethane Patch with Condensed ROS-Scavenging Backbone Units

Excessive reactive oxygen species (ROS) generated after myocardial infarction (MI) result in the oxidative injury in myocardium. Implantation of antioxidant biomaterials, without the use of any type of drugs, is very appealing for clinical translation, leading to the great demand of novel biomaterials with high efficiency of ROS elimination. In this study, a segmented polyurethane (PFTU) with a high density of ROS-scavenging backbone units is synthesized by the reaction of poly(thioketal) dithiol (PTK) and poly(propylene fumarate) diol (PPF) (soft segments), thioketal diamine (chain extender), and 1,6-hexamethylene diisocyanate (HDI). Its chemical structure is verified by gel permeation chromatography (GPC), ¹ H nuclear magnetic resonance (¹ H NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The electrospun composite PFTU/gelatin (PFTU/Gt) fibrous patches show good antioxidation capacity and ROS-responsive degradation in vitro. Implantation of the PFTU/gelatin patches on the heart tissue surface in MI rats consistently decreases the ROS level, membrane peroxidation, and cell apoptosis at the earlier stage, which are not observed in the non-ROS-responsive polyurethane patch. Inflammation and fibrosis are also reduced in the PFTU/gelatin-treated hearts, resulting in the reduced left ventricular remodeling and better cardiac functions postimplantation for 28 d.

A bioinspired Janus polyurethane membrane for potential periodontal tissue regeneration

Guided tissue regeneration (GTR) is the main therapeutic method for periodontal tissue regeneration. The key to the GTR strategy is the membrane which can assist the reconstruction of bone tissue in the periodontal defect and prevent the migration of epithelium and fibroblasts to the defect. However, the existing periodontal membrane cannot effectively promote periodontal tissue regeneration due to the limited bioactivity and physicochemical function. Here, we developed a bioinspired degradable polyurethane membrane with Janus surface morphology by integrating bioactive dopamine (DA) and an antibacterial Gemini quaternary ammonium salt (QAS). The Janus surface of the membrane is fabricated through spontaneous microphase separation, resulting from the different migration of functional segments between the air-contact upper surface with enriched antibacterial QAS and the substrate-contact bottom with enriched bioactive DA. The smooth surface of the upper membrane used to face the soft tissues can reduce cell adhesion to suppress the migration of fibroblasts, while the rough surface with a topological micro-pit structure of the bottom side facing the bone has excellent function of autonomic mineralization and cell adhesion to promote bone tissue reconstruction. In addition, the membrane containing the antibacterial QAS shows excellent antibacterial effect on common oral pathogens, such as S. aureus and S. mutans. Moreover, the specific dopamine group also endows the membrane with excellent antioxidant efficiency. In vivo research shows that this Janus polyurethane membrane can effectively promote periodontal tissue regeneration in a rat periodontal defect model. Combined with its excellent mechanical properties and biocompatibility, the polyurethane membrane is a promising material for potential periodontal tissue regeneration.